Method for producing a shaped body using a metal oxide sol

ABSTRACT

A process for producing a shaped body comprising at least one porous oxidic material and at least one metal oxide comprises the following step (i): 
     (i) mixing the porous oxidic material or materials with at least one metal oxide sol which has a low content of alkali metal and alkaline earth metal ions and/or at least one metal oxide which has a low content of alkali metal and alkaline earth metal ions.

This application is a 371 of PCT/EP99/02355 filed Apr. 7, 1999.

The present invention relates to a process for producing a shaped bodycomprising at least one porous oxidic material and at least one metaloxide, the shaped body per se and its use as catalyst in reactions oforganic compounds, in particular for the epoxidation of organiccompounds having at least one C—C double bond.

Shaped bodies which comprise porous oxidic materials are used innumerous chemical processes. This necessitates a production processwhich allows industrially relevant quantities of shaped bodies to beproduced inexpensively.

To produce shaped bodies, the porous oxidic material is generallyadmixed with a binder, an organic viscosity-increasing substance and aliquid for making the mixture into a paste and is densified in a kneaderor pan mill. The resulting mass is subsequently shaped by means of a ramextruder or screw extruder and the shaped bodies obtained are dried andcalcined.

In order to produce shaped bodies which are also suitable for producingvery reactive products, it is necessary to use chemically inert binderswhich prevent further reaction of these products.

Suitable binders are a series of metal oxides. Examples which may bementioned are oxides of silicon, of aluminum, of titanium or ofzirconium. Silicon dioxide as binder is disclosed, for example, in U.S.Pat. Nos. 5,500,199 and 4,859,785.

In such binders, the content of alkali metal and alkaline earth metalions should be as low as possible, which is why it is necessary to usebinder sources which are low in or free of alkali metals and alkalineearth metals.

To produce the abovementioned metal oxide binders, it is possible to usecorresponding metal oxide sols as starting materials. In the preparationof, for example, the abovementioned silicon dioxide binders which arelow in or free of alkali metals and alkaline earth metals, silica solwhich is low in or free of alkali metal and alkaline earth metals isemployed as binder source.

In the preparation of silica sols, it is possible to start from alkalimetal silicates, but this generally leads to undesirably high contentsof alkali metal ions in the silica sol. The preparation of such silicasols is described, for example, in “Ullmann's Encyclopedia of IndustrialChemistry”, volume A 23 (1993), pp. 614-629.

JP-A-07 048 117 discloses the preparation of silica sol by hydrolysis ofalkoxysilanes by means of ammonia in the presence of a large excess ofalcohol; the silica sols obtained contain up to 10% by weight of silicondioxide.

JP-A-05 085 714 describes the acid decomposition of alkoxysilanes,likewise in alcoholic medium. This gives silica sols having silicondioxide contents of from 1 to 10% by weight.

A disadvantage of the processes for preparing silica sols disclosed inthe latter two publications is the low silicon dioxide content which canbe achieved in the silica sols. This makes the process uneconomicalsince plant capacity is wasted by excess water both in sol productionand in further processing.

It is an object of the present invention to provide an industriallyusable process for producing shaped bodies which have a low content ofalkali metal and alkaline earth metal ions and can be used as catalysts,preferably in a fixed bed.

We have found that this object is achieved in a process for producingsuch shaped bodies by mixing porous oxidic material with metal oxide soland/or metal oxide in a first step of the process, where the metal oxidesol and the metal oxide each have a low content of alkali metal andalkaline earth metal ions.

The present invention accordingly provides a process for producing ashaped body comprising at least one porous oxidic material and at leastone metal oxide, which comprises the following step (i):

(i) mixing the porous oxidic material or materials with at least onemetal oxide sol which has a low content of alkali metal and alkalineearth metal ions and/or at least one metal oxide which has a low contentof alkali metal and alkaline earth metal ions.

The present invention likewise provides a shaped body which can beproduced by the above-described process and has a content of alkalimetal and alkaline earth metal ions of preferably less than 700 ppm,particularly preferably less than 600 ppm and in particular less than500 ppm.

In a preferred embodiment of the process of the present invention, themetal oxide sol is prepared by hydrolysis of at least one metallic acidester.

The present invention therefore also provides a process as describedabove in which the metal oxide sol is prepared by hydrolysis of at leastone metallic acid ester.

The metallic acid esters employed for the hydrolysis can be purifiedprior to the hydrolysis. All suitable methods are conceivable here.Preference is given to subjecting the metallic acid esters to adistillation prior to the hydrolysis.

For the hydrolysis of the metallic acid ester, all possible methods canbe used in principle. However, in the process of the present invention,the hydrolysis is preferably carried out in aqueous medium. This givesthe advantage that, compared to hydrolyses known from the literature,for example from JP 07,048,117 or JP 05,085,714, in which an excess ofalcohol is employed, significantly less alcohol has to be distilled off.

The hydrolysis can be catalyzed by addition of basic or acidicsubstances. Preference is given to basic or acidic substances which canbe removed by calcination without leaving a residue. Particularpreference is given to using substances selected from the groupconsisting of ammonia, alkylamines, alkanolamines, arylamines,carboxylic acids, nitric acid and hydrochloric acid. In particular,ammonia, alkylamines, alkanolamines and carboxylic acids are used.

The metallic acid esters used in the process of the present inventionare preferably esters of orthosilicic acid.

In the process of the present invention, the hydrolysis of the metallicacid esters is carried out at from 20 to 100° C., preferably from 60 to95° C., and at a pH of from 4 to 10, preferably from 5 to 9,particularly preferably from 7 to 9.

The molar ratio of catalytically active substance/metallic acid ester isgenerally from 0.0001 to 0.11, preferably from 0.0002 to 0.01 and inparticular from 0.0005 to 0.008.

In the process of the present invention, the hydrolysis gives metaloxide sols, preferably silica sols, which have a content of alkali metaland alkaline earth metal ions of less than 800 ppm, preferably less than600 ppm, more preferably less than 400 ppm, more preferably less than200 ppm, more preferably less than 100 ppm, particularly preferably lessthan 50 ppm, more particularly preferably less than 10 ppm, inparticular less than 5 ppm.

The present invention accordingly provides a metal oxide sol having acontent of alkali metal and alkaline earth metal ions of less than 800ppm which can be prepared by hydrolysis of at least one metallic acidester.

The metal oxide content of the metal oxide sols prepared according tothe present invention is generally up to 50% by weight, preferably from10 to 40% by weight.

The alcohol formed in the hydrolysis is generally distilled off in theprocess of the present invention. However, small amounts of alcohol canremain in the metal oxide sol as long as they do not adversely affectthe further steps of the process of the present invention.

An advantage for the industrial use of the metal oxide sols preparedaccording to the present invention is that they display no tendency toform gels. Specific precautionary measures for preventing gel formationare thus superfluous. The metal oxide sols prepared according to thepresent invention can be stored for a number of weeks, which makescoordination of the time at which they are prepared with furtherprocessing steps unproblematical.

In the process of the present invention, a mixture comprising at leastone porous oxidic material and at least one metal oxide is preparedusing a metal oxide sol prepared as described above as metal oxidesource.

In principle, there are no restrictions in respect of the method ofproducing the mixture. However, in the process of the present invention,preference is given to spraying a suspension comprising at least oneporous oxidic material and metal oxide sol.

Here, the amount of porous oxidic material present in the suspension issubject to no restrictions as long as the processability of thesuspension during preparation and spraying is ensured. The weight ratioof porous oxidic material to the metal oxide of the metal oxide sol ispreferably from 10 to 0.1, particularly preferably from 8 to 1.

The main constituents of the suspension are generally porous oxidicmaterial, metal oxide sol and water. The suspension can additionallycontain residual traces of organic compounds. These can originate, forexample, from the preparation of the porous oxidic material. Likewiseconceivable are alcohols which are formed in the hydrolysis of metallicacid esters or substances which are added as described above to promotethe hydrolysis of metallic acid esters.

Depending on the moisture content wanted in the mixture for furtherprocessing, drying can follow. Here, all conceivable methods can beemployed. Drying of the mixture is preferably carried out simultaneouslywith spraying in a spray drying step. The spray dryers are preferablyoperated using inert gases, particularly preferably nitrogen or argon.

As regards the porous oxidic materials which can be used in the processof the present invention for producing shaped bodies, there are noparticular restrictions as long as it is possible to produce shapedbodies as described herein from these materials and as long as thesematerials have the necessary catalytic activity.

The porous oxidic material is preferably a zeolite. Zeolites are, as isknown, crystalline aluminosilicates having ordered channel and cagestructures and containing micropores. For the purposes of the presentinvention, the term “micropores” corresponds to the definition in “PureAppl. Chem.” 57 (1985), p. 603-619, and refers to pores having a porediameter of less than 2 nm. The framework of such zeolites is built upof SiO₄ and AlO₄ tetrahedra which are connected via shared oxygen atoms.An overview of the known structures may be found, for example, in W. M.Meier, D. H. Olson and Ch. Baerlocher in “Atlas of Zeolite StructureTypes”, Elsevier, 4th Edition, London 1996.

There are also zeolites which contain no aluminum and in which theSi(IV) in the silicate lattice is partially replaced by titanium asTi(IV). The titanium zeolites, in particular those having a crystalstructure of the MFI type, and possible ways of preparing them aredescribed, for example, in EP-A 0 311 983 and EP-A 0 405 978. Apart fromsilicon and titanium, such materials can further comprise additionalelements such as aluminum, zirconium, tin, iron, niobium, cobalt,nickel, gallium, boron or small amounts of fluorine.

In the zeolites described, the titanium can be partially or completelyreplaced by vanadium, zirconium, chromium, niobium or iron or by amixture of two or more thereof. The molar ratio of titanium and/orvanadium, zirconium, chromium, niobium or iron to the sum of silicon andtitanium and/or vanadium, zirconium, chromium, niobium or iron isgenerally in the range from 0.01:1 to 0.1:1.

Titanium zeolites having an MFI structure are known for being able to beidentified by means of a particular X-ray diffraction pattern and alsoby means of a lattice vibration band in the infrared (IR) region atabout 960 cm⁻¹ and thus differing from alkali metal titanates orcrystalline and amorphous TiO₂ phases.

Preference is given to using titanium, vanadium, chromium, niobium orzirconium zeolites, more preferably titanium zeolites and in particulartitanium silicalites.

Specific examples are titanium, vanadium, chromium, niobium andzirconium zeolites having a pentasil zeolite structure, in particularthe types assigned by X-ray crystalography to the BEA, MOR, TON, MTW,FER, MFI, MEL, CHA, ERI, RHO, GIS, BOG, NON, EMT, HEU, KFI, FAU, DDR,MTT, RUT, RTH, LTL, MAZ, GME, NES, OFF, SGT, EUO, MFS, MWW or MFI/MELstructure and also ITQ-4. Zeolites of this type are described, forexample, in the abovementioned reference by Meier et al. Alsoconceivable for use in the process of the present invention aretitanium-containing zeolites having the UTD-1, CIT-1 or CIT-5 structure.Further titanium-containing zeolites are those having the ZSM-48 orZSM-12 structure.

Such zeolites are described, inter alia, in U.S. Pat.No. 5,430,000 andWO 94/29408, whose contents pertaining to this subject are fullyincorporated by reference into the present application. In the processof the present invention, particular preference is given to Ti zeoliteshaving an MFI, MEL or MFI/MEL structure.

Further preference is given to, specifically, the Ti-containing zeolitecatalysts which are generally referred to as “TS-1”, “TS-2”, “TS-3”, andalso Ti zeolites having a framework structure isomorphous withβ-zeolite.

The present invention accordingly provides a process for producing ashaped body as described above in which the porous oxidic material is azeolite.

Of course, it is also possible to use mixtures of two or more porousoxidic materials, in particular those mentioned above, in the process ofthe present invention.

The abovementioned titanium, zirconium, chromium, niobium, iron andvanadium zeolites are usually prepared by reacting an aqueous mixture ofa metal oxide source, preferably an SiO₂ source, and a titanium,zirconium, chromium, niobium, iron or vanadium source, e.g. titaniumoxide or an appropriate vanadium oxide, zirconium alkoxide, chromiumoxide, niobium oxide or iron oxide, and a nitrogen-containing organicbase as template, e.g. tetrapropylammonium hydroxide, if desired withfurther addition of basic compounds, in a pressure vessel at elevatedtemperature for a number of hours or a few days to give a crystallineproduct. This is filtered off, washed, dried and calcined at elevatedtemperature to remove the organic nitrogen base. In the powder obtainedin this way, at least some of the titanium or the zirconium, chromium,niobium, iron and/or vanadium is present within the zeolite framework invarying proportions with 4-, 5- or 6-coordination. To improve thecatalytic properties, this can be followed by repeated washing withhydrogen peroxide solution acidified with sulfuric acid, after which thetitanium or zirconium, chromium, niobium, iron and/or vanadium zeolitepowder has to be dried and calcined again. The titanium or zirconium,chromium, niobium, iron or vanadium zeolite powder prepared in this wayis used in the process of the present invention as a component of theabove-described suspension.

In particular, the present invention therefore provides a process asdescribed above in which the porous oxidic material or materials ismixed with at least one metal oxide sol, wherein the porous oxidicmaterial or materials is prepared by a process which comprises one ormore of the following steps (a) to (f):

(a) preparation of a preferably aqueous mixture of at least one metaloxide source, preferably an SiO₂ source, and a further metal source, forexample a titanium, zirconium, chromium, niobium, iron or vanadiumsource,

(b) crystallization of the mixture from (a) in a pressure vessel withaddition of at least one template compound, if desired with addition ofa further basic compound,

(c) drying of the crystalline product present in the suspensionresulting from (b), preferably by spray drying,

(d) calcination of the dried product from (c),

(e) comminution of the calcined product from (d), for example bymilling, to give particles having particle sizes of less than 500 μm,preferably less than 300 μm, particularly preferably less than 200 μm,

(f) if desired, repeated washing of the comminuted product from (e) withsubsequent drying and calcination.

With regard to the pore structure of the porous oxidic materials, too,there are no particular restrictions, i.e. the material can havemicropores, mesopores, macropores, micropores and mesopores, microporesand macropores, mesopores and macropores or micropores, mesopores andmacropores, where the definition of the terms “mesopores” and“macropores” likewise corresponds to that in the abovementionedreference in “Pure Appl. Chem.” and relates to pores having a diameterof from>2 nm to about 50 nm and of>about 50 nm, respectively.

However, preference is given to using microporous oxidic materials suchas titanium silicalites.

In a further preferred embodiment of the process of the presentinvention, the porous oxidic material or materials is mixed in step (i)with at least one metal oxide which has a low content of alkali metaland alkaline earth metal ions.

If the porous oxidic material is mixed with two or more metal oxides, itis possible to mix the porous oxidic material or materials with onemetal oxide first and to mix the resulting mixture with a further metaloxide. If desired, this mixture can then be mixed with a further metaloxide. Likewise, it is also possible to mix the porous oxidic materialwith a mixture of two or more metal oxides.

The alkali metal and alkaline earth metal content of this metal oxide orthe mixture of two or more metal oxides is generally less than 800 ppm,preferably less than 600 ppm, particularly preferably less than 500 ppmand in particular less than 200 ppm.

Such metal oxides having a low content of alkali metal and alkalineearth metal ions are, for example, pyrogenic metal oxides, for examplepyrogenic silica.

Of course, it is also possible to use conventional metal oxides in theprocess of the present invention, with the proviso that their content ofalkali metal and alkaline earth metal ions is appropriately low, asindicated above.

It is also possible, in the case of one or more conventional metaloxides which have a content of alkali metal and alkaline earth metalions which is higher than that specified above, to lower the content ofalkali metal and alkaline earth metal ions by washing, extraction orother suitable measures, likewise naturally by a combination of two ormore suitable measures, to such an extent that the metal oxides can beused in the process of the present invention.

Depending on the measure employed for lowering the content of alkalimetal and alkaline earth metal ions, it may be necessary to subject theconventional metal oxide or oxides to appropriate after-treatment. Forexample, if the content of alkali metal and alkaline earth metal ions ofa conventional metal oxide is reduced by washing, it is sometimesnecessary to dry the conventional metal oxide after washing before it ismixed with the porous oxidic material or materials.

In the process of the present invention, it is naturally also possibleto mix the mixture resulting from mixing the porous oxidic material ormaterials with the metal oxide with at least one metal oxide sol whichhas a low content of alkali metal and alkaline earth metal ions. Asregards the preparation of this mixture, there are in principle norestrictions, as in the case of the preparation of the mixture of porousoxidic material and metal oxide sol, as described above. However,preference is given to spraying a suspension comprising the mixture ofthe porous oxidic material or materials and the metal oxide or oxidesand the metal oxide sol or sols. As regards the amount of porous oxidicmaterial present in this suspension, there are no restrictions as longas, as described already above, the processability of the suspension isensured.

Furthermore, it is naturally also possible, in the process of thepresent invention, to mix a mixture resulting from mixing at least oneporous oxidic material with at least one metal oxide sol with at leastone metal oxide which has a low content of alkali metal and alkalineearth metal ions. Here, mixing with the metal oxide or oxides canimmediately follow the preparation of the mixture of the porous oxidicmaterial or materials and the metal oxide sol or sols. Should, asalready described above, drying be necessary after the preparation ofthe mixture of the porous oxidic material or materials and the metaloxide sol or sols, it is also possible to mix the metal oxide with thedried mixture after drying.

In the process of the present invention, it is likewise possible to mixthe porous oxidic material or materials simultaneously with at least onemetal oxide sol and at least one metal oxide.

The mixture obtained after one of the above-described embodiments of theinvention is densified in a further stage of the process of the presentinvention. In this densification or shaping step, further metal oxidecan, if desired, be introduced using a metal oxide sol prepared asdescribed above as metal oxide source. This processing step can becarried out in all suitable apparatuses, although kneaders, pan mills orextruders are preferred. For industrial use of the process of thepresent invention, particular preference is given to using a pan mill.

If, according to an embodiment which has already been described above, amixture of at least one porous oxidic material and at least one metaloxide is prepared first and this mixture is densified and metal oxidesol having a low content of alkali metal and alkaline earth metal ionsis additionally added in the densification step, then, in a preferredembodiment of the present invention, from 20 to 80% by weight of porousoxidic material, from 10 to 60% by weight of metal oxide and from 5 to30% by weight of metal oxide sol are used. Particular preference isgiven to using from 40 to 70% by weight of porous oxidic material, from15 to 30% by weight of metal oxide and from 10 to 25% by weight of metaloxide sol. These percentages by weight are in each case based on theshaped body produced in the end, as described below. Preference is heregiven to using porous oxidic titanium-containing material and silicasol.

In a further embodiment of the process of the present invention, themixing of the porous oxidic material or materials with the metal oxideor oxides having a low content of alkali metal and alkaline earth metalions is carried out during the densification step. Accordingly, it islikewise possible to mix the porous oxidic material or materials, themetal oxide or oxides and additionally at least one metal oxide sol inthe densification step.

In this shaping step it is also possible to add one or moreviscosity-increasing substances as materials for making the mixture intoa paste; these substances may serve, inter alia, to increase thestability of the uncalcined shaped body, as described below. For thispurpose, it is possible to use all suitable substances known from theprior art. In the process of the present invention, water or mixtures ofwater with one or more organic substances, provided that they aremiscible with water, are used for making the mixture into a paste. Thematerials used for making the mixture into a paste can be removed againduring the later calcination of the shaped body.

Preference is given to using organic, in particular hydrophilic organic,polymers such as cellulose, cellulose derivatives, for examplemethylcellulose, ethylcellulose or hexylcellulose, polyvinylpyrrolidone,ammonium (meth)acrylates, Tylose or mixtures of two or more thereof.Particular preference is given to using methylcellulose.

As further additives, it is possible to add ammonium, amines oramine-like compounds such as tetraalkylammonium compounds oraminoalkoxides. Such further additives are described in EP-A 0 389 041,EP-A 0 200 260 and WO 95/19222, which in this respect are fullyincorporated by reference into the present application.

Instead of basic additives, it is also possible to use acidic additives.Preference is given to organic acidic compounds which can be burned outby calcination after the shaping step. Particular preference is given tocarboxylic acids.

The amount of these auxiliaries is preferably from 1 to 10% by weight,particularly preferably from 2 to 7% by weight, in each case based onthe shaped body produced in the end, as described below.

To influence properties of the shaped body such as transport porevolume, transport pore diameter and transport pore distribution, it ispossible to add further substances, preferably organic compounds, inparticular organic polymers, as further additives which can alsoinfluence the shapeability of the composition. Such additives includealginates, polyvinylpyrrolidones, starch, cellulose, polyethers,polyesters, polyamides, polyamines, polyimines, polyalkenes,polystyrene, styrene copolymers, polyacrylates, polymethacrylates, fattyacids such as stearic acid, high molecular weight polyalkylene glycolssuch as polyethylene glycol, polypropylene glycol or polybutyleneglycol, or mixtures of two or more thereof. The total amount of thesematerials, based on the shaped body produced in the end, as describedbelow, is preferably from 0.5 to 10% by weight, particularly preferablyfrom 1 to 6% by weight.

The present invention accordingly also provides for the use ofpolyalkylene glycol, in particular polyethylene glycol, in theproduction of shaped bodies comprising titanium silicalite, particularlythose which are used as catalysts for selective oxidation.

In a preferred embodiment, the process of the present invention is usedto produce shaped bodies which are essentially microporous but canadditionally have mesopores and/or macropores. The pore volume of themesopores and macropores in the shaped body of the present invention,determined in accordance with DIN 66133 by mercury porosimetry, isgreater than 0.1 ml/g, preferably greater than 0.2 ml/g, particularlypreferably greater than 0.3 ml/g, in particular greater than 0.5 ml/g.

The order of addition of the above-described additives to the mixturewhich has been obtained by one of the abovedescribed methods is notcritical. It is equally possible to introduce firstly further metaloxide via a metal oxide sol, subsequently the viscosity-increasingsubstances and then the substances which influence the transportproperties and/or the shapeability of the densified composition or toimply any other order desired.

Prior to the densification, the generally still pulverulent mixture can,if desired, be homogenized in the kneader or extruder for from 10 to 180minutes. This is generally carried out at a temperature in the rangefrom about 10° C. to the boiling point of the material for making themixture into a paste and at atmospheric pressure or slightlysuperatmospheric pressure. The mixture is kneaded until an extrudablemass has been formed.

The composition which has been obtained from the densification step andis now ready for shaping has, in the process of the present invention, ametal oxide content of at least 10% by weight, preferably at least 15%by weight, particularly preferably at least 20% by weight, in particularat least 30% by weight, based on the total composition. Particularlywhen using titanium-containing microporous oxides, the compositionproduced in the process of the present invention leads to no problemscaused by thixotropic properties in the subsequent shaping step.

In principle, kneading and shaping can be carried out using allconventional kneading and shaping equipment or methods which are wellknown from the prior art and are suitable for producing, for example,shaped catalyst bodies.

Preference is given to using methods in which shaping is carried out byextrusion in customary extruders, for example to produce extrudateshaving a diameter of usually from about 1 to about 10 mm, in particularfrom about 1.5 to about 5 mm. Such extrusion equipment is described, forexample, in “Ullmanns Enzyklopädie der Technischen Chemie”, 4th edition,vol. 2 (1972), p. 295 ff. Apart from the use of a screw extruder,preference is likewise given to using a ram extruder. In the case of alarge-scale industrial application of the process, particular preferenceis given to using screw extruders.

The extrudates are either extruded rods or honeycombs. The honeycombscan have any desired shape. They can be, for example, round extrudates,hollow extrudates or star-shaped extrudates. The honeycombs can alsohave any diameter. The external shape and the diameter are generallydecided by process engineering requirements which are determined by theprocess in which the shaped bodies are to be used.

Before, during or after the shaping step, noble metals in the form ofsuitable noble metal components, for example in the form ofwater-soluble salts, can be applied to the material. Such a process ispreferably employed to produce oxidation catalysts based on titaniumsilicates or vanadium silicates having a zeolite structure, making itpossible to obtain catalysts which contain from 0.01 to 30% by weight ofone or more noble metals selected from the group consisting ofruthenium, rhodium, palladium, osmium, iridium, platinum, rhenium, goldand silver. Such catalysts are described, for example, in DE-A 196 23609.6 which is hereby, in respect of the catalysts described therein,fully incorporated by reference into the present application.

In many cases, however, it is most expedient to apply the noble metalcomponents to the shaped bodies only after the shaping step,particularly when a high-temperature treatment of the catalystcomprising noble metal(s) is undesirable. The noble metal componentscan, in particular, be applied to the shaped body by ion exchange,impregnation or spraying-on. Application can be carried out usingorganic solvents, aqueous ammoniacal solutions or supercritical phasessuch as carbon dioxide.

The use of the above-described methods enables a wide variety ofcatalysts comprising noble metals to be produced. Thus, a type of coatedcatalyst can be produced by spraying the noble metal solution onto theshaped bodies. The thickness of this coating or shell comprising noblemetal(s) can be significantly increased by impregnation, while in thecase of ion exchange the catalyst particles are essentially uniformlyloaded with noble metal across the entire cross section of the shapedbody.

After extrusion by means of a ram extruder or a screw extruder, theshaped bodies obtained are dried for from about 1 to 20 hours atgenerally from 50 to 250° C., preferably from 80 to 250° C., atpressures of generally from 0.01 to 5 bar, preferably from 0.05 to 1.5bar.

The subsequent calcination is carried out at from 250 to 800° C.,preferably from 350 to 600° C., particularly preferably from 400 to 500°C. The pressure range employed is similar to that for drying. Ingeneral, the calcination is carried out in an oxygen-containingatmosphere, with the oxygen content being from 0.1 to 90% by volume,preferably from 0.2 to 22% by volume, particularly preferably from 0.2to 10% by volume.

The present invention thus also provides a process for producing shapedbodies, as described above, which comprises the following steps (i) to(v):

(i) mixing the porous oxidic material or materials with at least onemetal oxide sol which has a low content of alkali metal and alkalineearth metal ions and/or at least one metal oxide which has a low contentof alkali metal and alkaline earth metal ions;

(ii) densifying the mixture from step (i), if desired with addition ofmetal oxide sol;

(iii) shaping the composition from step (ii);

(iv) drying the shaped bodies from step (iii);

(v) calcining the dried shaped bodies from step (iv). In a specificembodiment of the invention, the metal oxide sol is added to thesuspension obtained from the step (b) described further above, theresulting suspension is dried, preferably by spray drying, and theresulting powder is calcined. The dried and calcined product can then befurther processed as per step (iii).

Of course, the extrudates obtained can be further processed. All methodsof comminution, for example by crushing or breaking the shaped bodies,are conceivable, as are further chemical treatments as, for example,described above. If comminution takes place, preference is given toproducing granules or chips having a particle diameter of from 0.1 to 5mm, in particular from 0.5 to 2 mm.

These granules or chips as well as shaped bodies produced in another waycontain virtually no finer particles than those having a minimumparticle diameter of about 0.1 mm.

The shaped bodies of the present invention or produced according to thepresent invention can be used as catalysts, in particular for catalyticconversion, especially for the oxidation of organic molecules. Examplesof possible reactions are:

the epoxidation of olefins, e.g. the preparation of propene oxide frompropene and H₂O₂ or from propene and mixtures which yield H₂O₂ in situ;

hydroxylations such as the hydroxylation of monocyclic, bicyclic orpolycyclic aromatics to give monosubstituted, disubstituted orhigher-substituted hydroxyaromatics, for example the reaction of phenoland H₂O₂ or of phenol and mixtures which yield H₂O₂ in situ to givehydroquinone;

the conversion of alkanes into alcohols, aldehydes and acids;

oxime formation from ketones in the presence of H₂O₂ or mixtures whichyield H₂O₂ in situ and ammonia (ammonoximation), for example thepreparation of cyclohexanone oxime from cyclohexanone;

isomerization reactions such as the conversion of epoxides intoaldehydes;

and also further reactions described in the literature as beingcatalyzed by such shaped bodies, in particular zeolite catalysts, as aredescribed, for example, by W. Hölderich in “Zeolites: Catalysts for theSynthesis of Organic Compounds”, Elsevier, Stud. Surf. Sci. Catal., 49,Amsterdam (1989), pp. 69-93, and in particular for possible oxidationreactions as described by B. Notari in Stud. Surf. Sci. Catal., 37(1987), pp. 413-425, or in Advances in Catalysis, vol. 41, AcademicPress (1996), pp. 253-334.

The present invention therefore provides for the use of one of theshaped bodies produced as described above or a mixture of two or morethereof as a catalyst.

The zeolites which have been extensively discussed above areparticularly suitable for the epoxidation of alkenes.

The present invention accordingly also provides a process for preparingat least one alkene oxide, which comprises the following step (III):

(III) reaction of at least one alkene with hydrogen peroxide over acatalyst which is a shaped body produced by a process as described aboveor a shaped body as described above.

Alkenes which are possibilities for such functionalization byepoxidation are, for example, ethene, propene, 1-butene, 2-butene,isobutene, butadiene, pentenes, piperylene, hexenes, hexadienes,heptenes, octenes, diisobutene, trimethylpentene, nonenes, dodecene,tridecene, tetra- to eicosenes, tri- and tetrapropene, polybutadienes,polyisobutenes, isoprene, terpenes, geraniol, linalool, linalyl acetate,methylenecyclopropane, cyclopentene, cyclohexene, norbomene,cycloheptene, vinylcyclohexane, vinyloxirane, vinylcyclohexene, styrene,cyclooctene, cyclooctadiene, vinylnorbornene, indene, tetrahydroindene,methylstyrene, dicyclopentadiene, divinylbenzene, cyclododecene,cyclododecatriene, stilbene, diphenylbutadiene, vitamin A,beta-carotene, vinylidene fluoride, allyl halides, crotyl chloride,methallyl chloride, dichlorobutene, allyl alcohol, methallyl alcohol,butenols, butenediols, cyclopentenediols, pentenols, octadienols,tridecenols, unsaturated steroids, ethoxyethene, isoeugenol, anethole,unsaturated carboxylic acids such as acrylic acid, methacrylic acid,crotonic acid, maleic acid, vinylacetic acid, unsaturated fatty acidssuch as oleic acid, linoleic acid, palmitic acid, naturally occurringfats and oils.

The zeolites which have been extensively discussed above areparticularly suitable for the epoxidation of alkenes having from 2 to 8carbon atoms, more preferably ethene, propene or butene and inparticular propene, to give the corresponding alkene oxides.

Accordingly, the present invention provides, in particular, for the useof the shaped body described herein as catalyst for preparing propeneoxide starting from propene and hydrogen peroxide or from propene andmixtures which yield H₂O₂ in situ.

In a specific embodiment of the process, the alkene to be epoxidized isprepared by dehydrogenation of the corresponding alkane.

Accordingly, the present invention also provides a process as describedabove which comprises the additional step (I):

(I) preparation of the alkene or alkenes reacted in step (III) bydehydrogenation of at least one alkane.

This dehydrogenation can, in principle, be carried out by all methodsknown from the prior art. Such methods are described, inter alia, inEP-A 0 850 936 which in this respect is fully incorporated by referenceinto the present application.

In a preferred embodiment of the process of the present invention, thehydrogen which is generated in the dehydrogenation of the alkane oralkanes is used for preparing the hydrogen peroxide with which thealkene or alkenes produced in the dehydrogenation is reacted in step(III).

Accordingly, the present invention also provides a process as describedabove which comprises the following step (II):

(II) reaction of the hydrogen formed in step (I) to give hydrogenperoxide, where the hydrogen peroxide is used for the reaction in step(III).

The present invention accordingly also provides an integrated processfor preparing an alkene oxide which comprises the steps (A) to (C):

(A) dehydrogenation of an alkane to give an alkene and hydrogen,

(B) reaction of the hydrogen obtained in (A) to give hydrogen peroxide,and

(C) reaction of the hydrogen peroxide from (B) with the alkene from (A)to give the alkene oxide using a shaped body according to the presentinvention.

The reaction of the hydrogen to give hydrogen peroxide can be carriedout by all methods which are known from the prior art. In particular,the hydrogen can be reacted with molecular oxygen to give hydrogenperoxide. It is likewise conceivable to prepare hydrogen peroxide usingthe hydrogen from step (A) by means of the anthraquinone process. Inboth cases, it may be necessary to purify the hydrogen from step (A)before further use. Preference is, however, given to using theanthraquinone process. This is based on the catalytic hydrogenation ofan anthraquinone compound to give the corresponding anthrahydroquinonecompound, subsequent reaction of this with oxygen to form hydrogenperoxide and subsequent isolation of the hydrogen peroxide formed byextraction. The catalysis cycle is closed by rehydrogenation of theanthraquinone compound which is obtained back in the reaction withoxygen. An overview of the anthraquinone process is given in “Ullmann'sEncyclopedia of Industrial Chemistry”, 5th edition, volume 13, pages 447to 456.

When using one or more shaped bodies produced according to the presentinvention as catalyst, the latter can, when deactivated, be regeneratedby a process in which the regeneration is carried out by targetedburning-off of the deposits responsible for deactivation. This ispreferably carried out in an inert gas atmosphere containing preciselydefined amounts of substances which act as an oxygen source. Thisregeneration process is described in DE-A 197 23 949.8, the relevantcontent of which are fully incorporated by reference into the presentapplication.

In addition, the present invention in its most general embodimentprovides for the use of a metal oxide sol prepared as described above asbinder for producing a shaped body having high chemical resistance andmechanical strength.

The following examples illustrate the invention.

EXAMPLES Example 1

Preparation of a Microporous Oxidic Material

910 g of tetraethyl orthosilicate were placed in a four-neck flask (4 lcapacity) and 15 g of tetraisopropyl orthotitanate were added from adropping funnel over a period of 30 minutes while stirring (250 rpm,blade stirrer). A colorless, clear mixture was formed. 1600 g of a 20%strength by weight tetrapropylammonium hydroxide solution (alkali metalcontent<10 ppm) were subsequently added and the mixture was stirred foranother 1 hour. The alcohol mixture formed by the hydrolysis (about 900g) was distilled off at 90-100° C. 3 l of water were added and the nowslightly opaque sol was transferred to a 5 l capacity stirring autoclavemade of stainless steel.

The closed autoclave (anchor stirrer, 200 rpm) was brought to a reactiontemperature of 175° C. at a heating rate of 3° C./min. The reaction wascomplete after 92 hours. The cooled reaction mixture (white suspension)was centrifuged and the solid was washed a number of times with wateruntil neutral. The solid obtained was dried at 110° C. for 24 hours(weight: 298 g). The template remaining in the zeolite was subsequentlyburned off in air at 550° C. for 5 hours (calcination loss: 14% byweight).

The pure white product had, according to wet chemical analysis, a Ticontent of 1.5% by weight and a residual alkali metal content of lessthan 100 ppm. The yield based on silicon dioxide used was 97%. Thecrystalites had a size of from 0.05 to 0.25 μm and the product displayeda typical band at about 960 cm⁻¹ in the IR spectrum.

Example 2

Preparation of a Silica Sol

3 l of water were placed in a 10 l four-neck flask provided withstirrer, thermometer and reflux condenser. The pH of the solution wasadjusted to 8-9 using 6 g of 25% strength ammonia. The water wassubsequently heated to 50° C. and 1300 g of tetraethyl orthosilicatewere added from a dropping funnel.

The mixture of water and tetraethyl orthosilicate was refluxed for 3hours. A further 1304 g of tetraethyl orthosilicate were then added viaa dropping funnel. After refluxing for another 2 hours, the resultingsilica sol/water mixture was stirred for a further 12 hours and theethanol formed by hydrolysis was then distilled off.

The 3618 g of silica sol produced in this way had a silicon dioxidecontent of about 20% by weight and a content of alkali metal ions ofless than 3 ppm.

Example 3

Preparation of a Silica Sol

188.6 g of water were placed in a 500 ml four-neck flask provided withstirrer, thermometer and reflux condenser. The pH of the solution wasadjusted to 9 using 0.3 g of 25% strength ammonia. The water wassubsequently heated to 50° C. and 111.65 g of tetraethyl orthosilicatewere added from a dropping funnel.

The mixture of water and tetraethyl orthosilicate was refluxed for 2hours. A further 111.65 g of tetraethyl orthosilicate were then addedvia a dropping funnel. After refluxing for another 2 hours, theresulting silica sol/water mixture was refluxed for another 12 hours. 50g of water were subsequently added and the ethanol formed by hydrolysiswas then distilled off.

The 169 g of silica sol produced in this way had a silicon dioxidecontent of about 38% by weight and a content of alkali metal ions ofless than 5 ppm.

Example 4

Spraying of Titanium Silicalite

200 g of milled catalyst, prepared as described in Example 1, were firstfinely milled to a particle size of<300 μm and then suspended in 2000 gof water. 245 g of aqueous silica sol having a silicon dioxide contentof 18% by weight, prepared as described in Example 2, were subsequentlymixed in.

While stirring continually, the suspension was pumped by means of aperistaltic pump into a laboratory spray dryer made of glass (diameter:200 mm, height of the cylindrical section: 500 mm) and atomized by meansof a two-fluid nozzle (diameter of the liquid feed line: 2.5 mm,admission pressure of gas to nozzle: 3 bar).

In the spray dryer, the suspension was dried by means of the drying gas(nitrogen, throughput: 24 kg/h, inlet temperature: 210° C., outlettemperature: 100° C.) to give a fine, intimately mixed powder which wasthen separated out in a glass cyclone. The yield was 80%.

Example 5

Spraying of Titanium Silicalite

16.1 kg of catalyst, prepared as described in Example 1, were firstcoarsely milled in a hammer mill and then finely milled to a particlesize of<300 μm using an impeller breaker.

The powder was subsequently suspended in 160 l of water with addition of16 kg of aqueous silica sol having a silicon dioxide content of 20% byweight, prepared as described in Example 2, and placed in an openstirred vessel. While stirring continually, the suspension was taken offby means of a large peristaltic pump and dried in a spray drying unit(from Niro) to give a fine, intimately mixed powder.

The suspension was atomized using an atomizer disk with ceramic bushes(rotational speed: 17,000 rpm). Drying was carried out at an air inlettemperature of 260° C. and an air outlet temperature of 110° C.

The product was separated off from the stream of air in a cyclone. Theyield was 13 kg.

Comparative Example 1

Shaping of Titanium Silicalite (Catalyst A)

Catalyst A was produced by mixing 1665 g of a spray-dried powderconsisting of 89% by weight of a catalyst prepared as described inExample 1 and 11% by weight of silicon dioxide with 416 g of a silicasol having a silicon dioxide content of about 50% by weight (Ludox™ fromDuPont). The spray-dried powder specified was prepared as described inExample 4 except that a commercially produced silica sol (Ludox AS-40from DuPont) having a sodium content of 800 ppm was used in place of thesilica sol prepared according to the present invention.

The mixture was made extrudable by addition of water and the extrusionaid methylcellulose and was extruded to give extrudates having adiameter of 1.5 mm.

These extrudates were dried at 120° C. and heated at 500° C. for 5hours. The silicon dioxide binder content of the shaped body was 20% byweight, the sodium content was 700 ppm.

Comparative Example 2

Shaping of Titanium Silicalite (Catalyst B)

Catalyst B was produced by mixing 3000 g of a spray-dried powderconsisting of 78% by weight of a catalyst prepared as described inExample 1 and 22% by weight of silicon dioxide with 750 g of a silicasol having a silicon dioxide content of about 43% by weight (Ludox AS-40from DuPont).

The spray-dried powder specified was prepared as described in Example 4except that a commercially produced silica sol (Ludox AS-40 from DuPont)having a sodium content of 800 ppm was used in place of the silica solprepared according to the present invention.

The mixture was made extrudable by addition of water and the extrusionaid methylcellulose and was extruded to give extrudates having adiameter of 2.5 mm.

These extrudates were dried at 120° C. and heated at 500° C. for 5hours. The silicon dioxide binder content of the shaped body was 30% byweight, the sodium content was 910 ppm. The lateral compressive strengthof the extrudates was 37.9 N, the cutting resistance was 10.25 N.

Comparative Example 3

Shaping of Titanium Silicalite (Catalyst C)

Catalyst C was produced by mixing 7500 g of a spray-dried powderconsisting of 78% by weight of a catalyst prepared as described inExample 1 and 22% by weight of silicon dioxide with 4300 g of a silicasol having a silicon dioxide content of about 43% by weight (Ludox AS-40from DuPont) in a pan mill.

The spray-dried powder specified was prepared as described in Example 4except that a commercially produced silica sol (Ludox AS-40 from DuPont)having a sodium content of 800 ppm was used in place of the silica solprepared according to the present invention.

The mixture was made extrudable by addition of water and the extrusionaid methylcellulose and was extruded to give extrudates having adiameter of 1.5 mm.

These extrudates were dried at 120° C. and heated at 500° C. for 5hours. The silicon dioxide binder content of the shaped body was 30% byweight, the sodium content was 900 ppm.

Example 6

Shaping of Titanium Silicalite (Catalyst D)

Catalyst D was produced by mixing 2200 g of a spray-dried powderconsisting of 75% by weight of a catalyst prepared as described inExample 1 and 25% by weight of silicon dioxide with 1037 g of a silicasol having a silicon dioxide content of about 21% by weight, prepared asdescribed in Example 2. The spray-dried powder specified was prepared bya method analogous to Example 4.

The mixture was made extrudable by addition of water and the extrusionaid methylcellulose and was extruded to give extrudates having adiameter of 1.5 mm.

These extrudates were dried at 120° C. and heated at 500° C. for 5hours. The silicon dioxide binder content of the shaped body was 32% byweight, the sodium content was 400 ppm.

Example 7

Shaping of Titanium Silicalite (Catalyst E)

Catalyst E was produced by mixing 9700 g of a spray-dried powderconsisting of 75% by weight of a catalyst prepared as described inExample 1 and 25% by weight of silicon dioxide with 13000 g of a silicasol having a silicon dioxide content of about 19% by weight, prepared asdescribed in Example 2, in a pan mill.

The spray-dried powder specified was prepared by a method analogous toExample 4.

The mixture was made extrudable by addition of water and the extrusionaid methylcellulose and was extruded to give extrudates having adiameter of 1.5 mm.

These extrudates were dried at 120° C. and heated at 500° C. for 5hours. The silicon dioxide binder content of the shaped body was 40% byweight, the sodium content was 420 ppm.

Example 8

The Shaping of Titanium Silicalite (Catalyst F)

Catalyst F was produced by mixing 8000 g of a spray-dried powderconsisting of 70% by weight of a catalyst prepared as described inExample 1 and 30% by weight of silicon dioxide with 4000 g of a silicasol having a silicon dioxide content of about 19% by weight, prepared asdescribed in Example 2, in a pan mill.

The spray-dried powder specified was prepared by a method analogous toExample 4.

The mixture was made extrudable by addition of water and the extrusionaid methylcellulose and was extruded to give extrudates having adiameter of 1.5 mm.

These extrudates were dried at 120° C. and heated at 500° C. for 5hours. The silicon dioxide binder content of the shaped body was 40% byweight, the sodium content was 400 ppm. The cutting resistance was 2 Nand the lateral compressive strength was 19 N.

Example 9

Densification and Shaping of Titanium Silicalite (Catalyst G)

3.5 kg of TS-1, prepared as described in Example 1, were densified in apan mill with 1.23 kg of Aerosil® (DEGUSSA), 6.26 kg of silica solprepared as described in Example 2 and 237 g of methylcellulose(Walocel®) for 60 minutes.

Subsequently 48 g of polyethylene glycol (ALKOX-E160®) were added, themixture was densified for a further 30 minutes, 96 g of polyethyleneglycol (ALKOX-E160®) and 450 g of deionized water were added and themixture was once more densified for 15 minutes.

The shapeable composition was shaped by means of an extruder to give 1.5mm round extrudates. The extrusion pressure was from 85 to 100 bar andthe extrusion time was 15 minutes. These extrudates were dried at 120°C. and calcined at 500° C. in air for 5 hours.

The yield was 5.1 kg. The silicon dioxide binder content of the shapedbody was 40% by weight, the sodium content was 500 ppm, the lateralcompressive strength was 17 N and the macropore volume was 0.70 g/ml,determined by Hg porosimetry in accordance with DIN 66133.

Example 10

Catalytic Trial (Batch Operation)

In each case, an amount of catalyst A to G corresponding to a mass oftitanium silicalite of 0.5 g was placed in a steel autoclave providedwith a basket insert and sparging stirrer.

The autoclave was charged with 100 g of methanol, closed and checked forabsence of leaks. The autoclave was subsequently heated to 40° C. and 11g of liquid propene were metered into the autoclave.

9.0 g of a 30% strength by weight aqueous hydrogen peroxide solutionwere then pumped into the autoclave by means of an HPLC pump and theremaining hydrogen peroxide in the feed lines was subsequently rinsedinto the autoclave using 16 ml of methanol. The initial hydrogenperoxide content of the reaction solution was 2.5% by weight.

After a reaction time of 2 hours, the autoclave was cooled and vented.The liquid product was analyzed cerimetrically for hydrogen peroxide.The propylene oxide content of the product was determined by gaschromatography.

The results of the analysis are summarized in the following table.

TABLE for Example 10 (Catalyst trial) Propylene oxide content Hydrogenperoxide of product content of product Catalyst % by weight % by weightA (comparative) 0.88 1.72 B (comparative) 0.86 1.74 C (comparative) 0.931.51 D 1.39 1.28 E 1.47 1.19 F 1.34 1.25 G 1.1 1.45

Example 11

Catalytic Test (Continuous Operation)

24 g/h of hydrogen peroxide (40% by weight), 57 g/h of methanol and 11.7ml/h of propene were passed at a reaction temperature of 40° C. and apressure of 20 bar through a tube reactor charged with 28.1 g of thecatalyst F according to the present invention.

After leaving the reactor, the reaction mixture was depressurizedagainst atmospheric pressure in a Sambay evaporator. The low boilerswhich were separated off were analyzed on-line in a gas chromatograph.The liquid reaction product was collected, weighed and likewise analyzedby gas chromatography.

The total reaction time was 550 hours. During this time, the hydrogenperoxide conversion was far above 90%. The selectivity of hydrogenperoxide to propylene oxide was likewise significantly more than 90%over the total period of time.

Example 12

Catalytic Test (Continuous Operation)

9 g/h of hydrogen peroxide (40% by weight), 49 g/h of methanol and 8 g/hof propene were passed at a reaction temperature of 40° C. and apressure of 20 bar through a tube reactor charged with 20 g of thecatalyst G according to the present invention.

After leaving the reactor, the reaction mixture was depressurizedagainst atmospheric pressure in a Sambay evaporator. The low boilerswhich were separated off were analyzed on-line in a gas chromatograph.The liquid reaction product was collected, weighed and likewise analyzedby gas chromatography.

The total reaction time was 850 hours. During this time, the hydrogenperoxide conversion was far above 90%. The selectivity of hydrogenperoxide to propylene oxide was likewise significantly more than 90%over the total period of time.

We claim:
 1. A process for producing a shaped body comprising at leastone porous oxidic material and at least one metal oxide, said processcomprising (i) mixing the porous oxidic material or materials with atleast one metal oxide sol which has a low content of alkali metal andalkaline earth metal ions and/or at least one metal oxide which has alow content of alkali metal and alkaline earth metal ions. (ii)densifying the mixture from step (i), (iii) shaping the composition fromstep (ii), (iv) drying the shaped body from step (iii), wherein themetal oxide sol has a content of alkali metal and alkaline earth metalions of less than 10 ppm.
 2. A process as claimed in claim 1 furthercomprising (v) calcining the dried shaped body from step (iv).
 3. Aprocess as claimed in claim 1, wherein the at least one metal oxide solis prepared by hydrolysis of at least one metallic acid ester.
 4. Aprocess as claimed in claim 3, wherein the metallic acid ester or estersis an ester of orthosilicic acid.
 5. A process as claimed in claim 1,wherein the porous oxidic material is a zeolite.